Conventionally, electronic components such as diodes, transistors, integrated circuits and the like are largely encapsulated by a cured product of an epoxy resin composition. Especially for the integrated circuits, epoxy resin compositions excellent in heat resistance and moisture resistance are used, the epoxy resin compositions containing an epoxy resin, a phenol resin type curing agent and an inorganic filler such as fused silica, crystalline silica or the like. In recent years, however, in the market trends of reduction in size, lightness and high functionality of electronic equipments, higher integration of semiconductor elements is increasing every year, and surface mounting of semiconductor devices is accelerated, and thus the requirements for heat resistance and moisture resistance of the epoxy resin compositions used for encapsulation of semiconductor elements are becoming stricter.
On the other hand, because the demand for cost reduction on semiconductor devices is also strict and the cost of the conventional gold wire connection is high, connection with use of metals other than gold such as aluminum, a copper alloy and copper is also employed. However, metals other than gold are still insufficient in the high temperature storage life and high temperature operating life under the high temperature environment having a temperature exceeding 150 degrees centigrade, which are especially demanded in the automotive applications, and the electrical reliability such as the moisture resistance reliability under the high temperature and high humidity environment having a temperature exceeding 60 degrees centigrade and a relative humidity exceeding 60%, in addition to the cost. Furthermore, in connection with a non-gold wire, there are problems such as migration, corrosion and rise in electrical resistance, and thus satisfactory devices have not always been obtained.
Especially, in the semiconductor devices using copper wires, there is a problem that copper is easy to corrode in a moisture resistance reliability test and thus lacks in reliability. Therefore, although copper wires have been successfully used as wires with a relatively large wire diameter for discrete power devices, it is currently difficult to employ copper wires for ICs requiring wires with a wire diameter of equal to or less than 25 μm, especially for single-sided encapsulated packages whose wires are even affected by impurities attributable to a circuit board.
Patent Document 1 proposes an approach to improve the processability of copper wires themselves to increase the reliability of bonding portions. Meanwhile, Patent Document 2 proposes an approach to increase the connection reliability by coating each of the copper wires with a conductive metal to prevent oxidation of copper wires. However, corrosion and electrical reliability such as moisture resistance reliability of a package encapsulated by a resin, that is, a semiconductor device itself are not accounted for.
On the other hand, a MAP molding becomes a mainstream, in which, in order to achieve downsizing, weight reduction and sophistication of packages, and improve the productivity, many semiconductor elements are molded at one time, and the elements are cut into pieces after molding to obtain respective elements. In a MAP molded product, in order to mold a large thin molded product, low viscosity, strength capable of withstanding cutting during segmenting into pieces, non-breaking, non-cracking flexibility, further low wearability with respect to a cutting blade and the like have been demanded for an encapsulating resin. In order to improve the reliability of the aforementioned package, it is preferable that an inorganic filler is highly filled in an encapsulating resin to reduce the moisture absorption ratio. However, there is a problem that due to high filling of the inorganic filler, cutting resistance is high and the blade is thus easily worn to damage the package stuck in the blade during segmenting into pieces in some cases. Accordingly, easiness of segmenting into pieces and low wearability with respect to a blade have been demanded for an encapsulating resin.